Here we use beer us an uncountable name for the type of drink. "A beer" is one glass or one bottle or one can or similar, but it does not fit this sentence well, I think.
I initially interpreted the English sentence as meaning "Where did he go to get beer" in the sense of, for example, where did he (just now) go to get beer, and I was confused by chodit in the Czech sentence. Now I'm thinking that the English meaning is more like, for example, where did he go to get beer... before he gave up drinking? Is this correct? Thanks!